netdev - Re: [PATCH v1 1/3] net: phy: Allow mdio buses to auto-probe c45 devices

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Message-ID: <20200622134429.GK1551@shell.armlinux.org.uk>
Date:   Mon, 22 Jun 2020 14:44:29 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Calvin Johnson <calvin.johnson@....nxp.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Jeremy Linton <jeremy.linton@....com>, Jon <jon@...id-run.com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        netdev@...r.kernel.org, linux.cj@...il.com
Subject: Re: [PATCH v1 1/3] net: phy: Allow mdio buses to auto-probe c45
 devices

On Mon, Jun 22, 2020 at 06:52:00PM +0530, Calvin Johnson wrote:
> On Wed, Jun 17, 2020 at 07:57:03PM +0100, Russell King - ARM Linux admin wrote:
> > On Wed, Jun 17, 2020 at 08:51:20PM +0200, Andrew Lunn wrote:
> > > > > +	/* bus capabilities, used for probing */
> > > > > +	enum {
> > > > > +		MDIOBUS_C22 = 0,
> > > > > +		MDIOBUS_C45,
> > > > > +		MDIOBUS_C22_C45,
> > > > > +	} probe_capabilities;
> > > > 
> > > > I think it would be better to reserve "0" to mean that no capabilities
> > > > have been declared.  We hae the situation where we have mii_bus that
> > > > exist which do support C45, but as they stand, probe_capabilities will
> > > > be zero, and with your definitions above, that means MDIOBUS_C22.
> > > > 
> > > > It seems this could lock in some potential issues later down the line
> > > > if we want to use this elsewhere.
> > > 
> > > Hi Russell
> > > 
> > > Actually, this patch already causes issues, i think.
> > > 
> > > drivers/net/ethernet/marvell/mvmdio.c contains two MDIO bus master
> > > drivers. "marvell,orion-mdio" is C22 only. "marvell,xmdio" is C45
> > > only. Because the capabilites is not initialized, it will default to
> > > 0, aka MDIOBUS_C22, for the C45 only bus master, and i expect bad
> > > things will happen.
> > > 
> > > We need the value of 0 to cause existing behaviour. Or all MDIO bus
> > > drivers need reviewing, and the correct capabilities set.
> > 
> > Yes, that's basically what I was trying to say, thanks for putting it
> > more clearly.
> 
> Prior to this patch, below code which is for C22 was executed in this path.
> 	phydev = get_phy_device(bus, addr, false);
> Doesn't this mean that MDIOBUS_C22 = 0, doesn't break anything?

Please re-read Andrew's email that you quoted above, and consider this
point: If bus->probe_capabilities == MDIOBUS_C22 for the Marvell XMDIO
device, as it _will_ be the case, because bus->probe_capabilities has
not been set, is this a sane situation?

Are you willing to do a full audit of all MDIO drivers and set their
bus->probe_capabilities correctly in every case in order to use
MDIOBUS_C22 = 0 ?

-- 
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